Insights from Studies on Ambient Particulate Matter Engineered nanomaterials (ENMs) are now being developed for a wide range of applications, used in engineering, medicine, sports goods and the leisure industry, and for domestic use such as in cosmetics, clothing, and food. Any biological effects of these novel materials might be expected to reflect their chemistry. However, because the nano-sized particles are transitional, between the atomic molecular components and that of the bulk material, they exhibit extraordinary properties which make it difficult to predict their reactivity simply on the basis of their chemistry. Thus, unique features that make ENMs very attractive for use in novel applications, may also have adverse health effects. There are increasing concerns from prestigious societies (1), government bodies, academic institutes and other organisations, that these new products will result in adverse effects in biological systems (2-5). Initial concern stemmed from epidemiological studies showing that increased cardiorespiratory morbidity and mortality during episodes of air pollution (5-8,13), correlated with increases in the numbers of nanosized particles, particularly diesel exhaust, in the atmosphere. Those with existing lung disease, such as asthma, chronic obstructive pulmonary disease and cancer, were most susceptible. Only a small increase (10 micrograms/meter3) in the amount of ambient particulate matter less that 10 microns (PMio) or 2.5 microns (PM2.5) aerodynamic diameter is needed to increase the risk of myocardial infarct. Other cardiovascular effects include reduced heart rate variability, raised blood pressure and atherosclerosis. Whilst one might anticipate that inhalation of particulate air pollution might have adverse effects on the lung, the cardiovascular effects are surprising and suggest that events taking place within the pulmonary system can cascade into other body systems. These studies highlight the critical role of the lung defence mechanisms in protection from inhaled toxicants. They also highlight the importance ofthe lung as a target organ for atmospheric particulate pollution and the need to understand the mechanisms involved in breaching the pulmonary defence system, in order to manage any risks and hazards of atmospheric exposure to ENM.